well i had just one of these 12s in a prefab box that for some reason had 2 ports with different tunning. it had 1 earo port that was suppose to be at 38hz and then its had a second chamer inside the box that looked kinda like a L shape slot port but then that chamber was ported with a earo port at 42 hz. that peaked at 48hz. then i had a box with to small of port erea tuned to 41 hz that peaked at 45hz ( 1 12 here to ). the box was built using the box design in the manual for the sub. but the guy that i know at the shop i go to knows a lot about rockford and talked to the rockford tech and they agreed with a slot port like my design it would be loudest at or near 43-45hz.

I wouldnt go ABC box just cause of the rule of thumbness about it. As far as I know there isnt really math out there for you to go by at least the last time I checked. Im still thinking you should do a aero port box. Keep one set of ports that are tuned to the peak frequency of your car for when you compete and then another set for daily.

I sure as help hope you go up more than 1db from going to a pre fab to a custom box. I hate to nut hug but look up PWK designs they are 50 dollars. but he will use his software and take your given cabin geometry your subwoofers T/S parameters and then model different kinds of enclosures untill he finds you desired response. Which would be the loudest possible at your cars peak. might be worth it. Of course you can download the same software he is using but it will take you quite a while to figure out how to use it correcty

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